Design of SIMO M-QAM System for Ultrasonic Communications on Shallow Waters

Abstract

In this work, we present a transmission system that uses single-carrier modulation M-ary symbols quadrature amplitude modulation (M-QAM) for underwater acoustic communications (UAC) in the ultrasonic band. It exploits the diversity that four hydrophones provide at reception in a single-input multiple-output (SIMO) 1×4 configuration and also includes, for each stream, a phase-locked loop (PLL) for synchronization and a turbo-equalization subsystem, with fractionally-spaced equalizer (FSE) and decision feedback equalizer (DFE) filters, adaptive by means of least mean squares (LMS) algorithm, both of which are driven by an low-density parity check (LDPC) decoder decisions. The paper describes the system design and analyze its performances on trials carried out on shallow waters of the Mediterranean sea. Achievable data rates exceeding 200 kb/s between links of transmission distances longer than 200 m are obtained with a satisfactory low bit-error rate (BER).